The present invention relates generally to methods for producing detergents and more particularly to a method for producing a powdered detergent containing alpha olefin sulfonate.
Powdered detergents are used primarily for laundering purposes. A typical powdered laundry detergent contains surface-active agents, among other ingredients. Two typical surface-active agents are alkyl benzene sulfonate and alpha olefin sulfonate. In many cases it is desirable to incorporate both of these sulfonates into a detergent. Alpha olefin sulfonate is a less expensive detergent ingredient than alkyl benzene sulfonate. Therefore, it is desirable to incorporate into a powdered laundry detergent as much alpha olefin sulfonate as is practicable, while retaining alkyl benzene sulfonate also as an ingredient.
Alkyl benzene sulfonates and alpha olefin sulfonate are usually produced in substantially liquid form by neutralizing the corresponding sulfonic acid of each with a base, such as sodium hydroxide, to form sodium alkyl benzene sulfonate or sodium alpha olefin sulfonate. These substantially liquid sulfonates must then be dried before they can be incorporated into a powdered detergent. Conventionally, the liquid sulfonates are mixed with other ingredients which are to be incorporated into the powdered detergent, and these include both organic and inorganic ingredients. Many of these other ingredients are in solid powder form before being mixed with the liquid sulfonates, and the resulting mixture may be a slurry which is then subjected to a spray-drying operation, for example. In such a case, the slurry of detergent ingredients must contain sufficient liquid to permit pumping and spraying.
Conventionally, the spray-drying operation is conducted in a spray-drying tower within which the slurry is sprayed from the top and descends to the bottom. During the descent, the slurry is dried by hot gases rising from the bottom to the top of the tower. The dried detergent is withdrawn from the bottom in the form of a powder containing beads each of which includes essentially all of the ingredients of the detergent.
A drawback to mixing dry, powdery ingredients into a slurry, containing sufficient liquid to render the slurry pumpable and sprayable, is that ingredients which were once dry are heavily wetted and then have to be dried again, which is a waste of energy. However, it is necessary to heavily wet and then dry these normally powdery ingredients, in a process in which all of the liquid sulfonate is spray-dried, in order to incorporate all of the detergent ingredients into each of the individual beads of detergent in the final dry, powdered detergent product.
Exhaust gases removed from the top of the spray-drying tower are treated to separate carry-over powder particles therefrom and are then vented to the atmosphere. A problem arises when spray-drying a slurry containing alpha olefin sulfonate in that the gases vented from the top of the spray-drying tower contain offensive gaseous ingredients which pollute the air when vented into the atmosphere.
In another method for producing a powdered detergent, dry, powdered, inorganic ingredients of the detergent are introduced into the upstream end of a rotary drum mixer, and the dry, powdered material is advanced from the upstream to the downstream end, while being lifted and dropped as the rotary drum mixer rotates. As the dry, powdery material undergoes lifting and dropping, it is sprayed with liquid sulfonic acid and neutralizing agent, either through separate nozzles or through a mixing nozzle. The liquid sulfonate formed during the spraying, or during the mixing immediately preceding the spraying, is absorbed by the particles of powdered detergent ingredients already in the drum mixer and agglomerates them into composite particles, each containing essentially all of the ingredients introduced into the mixer.
A method of the type described in the preceding paragraph is disclosed in Pfrengle, U.S. Pat. No. 3,502,304. In such a method the sulfonate must contain sufficient liquid to facilitate spraying through nozzles. Because there is a limit on the amount of liquid sulfonate which can be sprayed onto the dry particles before the latter become too soggy, the sulfonate content of a powdered detergent product produced by such a procedure without subsequent drying is limited to a relatively low amount.